Gas membrane separation processes have received attention in recent years because of their capability of achieving energy conservation when used as a process for separating CO2 from various gases such as natural or exhaust gases as well as synthetic gases that are synthesized in large-scale plants for hydrogen or urea production.
Various separation membranes have been hitherto proposed as gas separation membranes for use in these gas membrane separation processes. For example, it is proposed in Japanese Patent Laying-Open No. 07-112122 (PTD 1) that a carbon dioxide separating gel membrane may be made of a hydrogel membrane formed by having an aqueous solution containing a carbon dioxide carrier absorbed in a vinyl alcohol-acrylic acid salt copolymer having a crosslinked structure. The invention of PTD 1 employs the vinyl alcohol-acrylic acid salt copolymer as a polymeric material that can hydrogelate by absorption of an aqueous solution containing a carbon dioxide carrier; this overcomes disadvantages of conventionally known polymer electrolytes such as polyacrylic acids that have high water absorption capacity but have poor strength that makes it difficult to obtain a membrane form. Thus, the invention of PTD 1 provides a carbon dioxide-facilitated transport membrane of practical use and a method for manufacturing the membrane.
Examples of gas separation membranes that employ a polyacrylic acid as a hydrogelable polymeric material include a CO2 separation film proposed in Japanese Patent Laying-Open No. 08-193156 (PTD 2), which film may be formed from a resin composition including a reaction mixture obtained by reacting a polyacrylic acid with a predetermined equivalent of aliphatic amine. It is proposed in Japanese Patent Laying-Open No. 2013-049048 (PTD 3) that a CO2-facilitated transport membrane may be made by depositing a gel layer onto a heat-resistant porous membrane, the gel layer having glycine and a deprotonating agent contained in a hydrogel membrane.